1. Field of the Invention
The present invention relates to novel aziridine compounds and to novel acrylic polymers having aziridine-containing structural moieties as pendant groups. The invention more specifically relates to coating compositions containing said acrylic polymers suitable for use where hardening of the coating composition at low temperatures, for example, ambient temperature, is required.
2. Brief Description of Prior Art
Known coating compositions which cure at low temperatures for use as automotive quality finishes, particularly as automotive refinishing compositions, include two-package compositions based on hydroxy-functional components and curing (crosslinking) agents containing isocyanate groups. However, the use of isocyanate-functional materials often requires that precautions be taken with respect to the handling and use of the isocyanates based on toxicity considerations. Such precautions can be relatively burdensome particularly when the coating compositions are utilized in environments not involving controlled factory conditions as exist, for example, in plants producing new automotive vehicles. For example, the application of automotive refinishing compositions tends to be done in refinishing shops under conditions which are not nearly as well controlled as those existing in automotive plants which manufacture original equipment. Accordingly, there is a need for high quality coating compositions which are not based on the utilization of isocyanate curing agents.
The present invention addresses these issues. The novel acrylic polymers bearing the pendant aziridine functional groups described and claimed in the present invention have been found to be useful in ambient temperature cured coatings. Surprisingly, the coatings have been found to be relatively non-toxic based on inhalation toxicology health data when compared to systems having known toxic behavior, for example, isocyanate-cured systems.
In U.S. Pat. No. 3,789,034 Wismer et al disclose the preparation of aziridine-functional polymers by preparing an aziridine-diisocyanate adduct and then reacting such adduct with hydroxy-bearing polymers. The aziridine-diisocyanate adduct is prepared, for example, by reacting a diisocyanate with 1,2-propylene imine in such a ratio so as to "half-block" the diisocyanate. Such a reaction does not lead solely to half-blocked products but also undesirable full-blocked products, which do not react with hydroxy-bearing polymers, and residual unreacted diisocyanate which will promote gelation when reacted with hydroxy-bearing polymers. Additionally, the products described by Wismer et al are urea-based, less reactive and do not possess the structure of any of the claimed subject matter herein.
Briden in U.S. Pat. No. 4,563,307 discloses the preparation of aziridine polymers, but not of the type claimed herein, involving the reaction of a specific isocyanate with an active hydrogen-containing aziridine.
In U.S. Pat. No. 4,656,217 Sugiura et al disclose a specific aziridine compound which is not consistent with the compounds claimed herein. Thus, the Sugiura et al compounds, ##STR2## are ureas, not urethanes.